The invention relates to an integrated semiconductor arrangement of the type for coupling between a photodetector D and a light wave guide G.sub.1, operating within a band of given wavelengths containing on the surface of a semiconductor substrate S of a III-V compound a confining layer C.sub.0 of a III-V compound and a transparent layer C.sub.1 of a III-V compound, transparent layer C.sub.1 being transparent for the operating wavelengths, and having an index superior to that of the confining layer, the light wave guide G.sub.1 being realized in layer C.sub.1, and also containing an absorbing layer C.sub.3 of a III-V compound for the operating wavelengths having an index superior to that of the waveguide, in which layer C.sub.3 the photodetector is realized.
The arrangement in accordance with the invention can be applied for detecting the output signal on one of the channels of an interferometer of the Mach-Zehnder type, for example, or on the output channels of an optical switching matrix, for controlling a negative feedback of the adjustment of the electrode voltage with a view to, for example, compensating for the undesired drift. This arrangement can also be used, for example, for fabricating bistable optical arrangements.
Such a coupling arrangement is known from the prior art from the publication by R. TROMMER in "Electronics Letters 25th Apr. 1985, Vol. 21, No. 9", entitled "Monolithic InGaAs Photodiode Array illuminated through an integrated waveguide". This document describes an array fabricated on top of a sulphur doped 100-oriented indium phosphide (InP) substrate, of the n.sup.+ type and having a thickness of 220 .mu.m , on one surface of which is fabricated an integrated waveguide and on the other surface of which is fabricated an indium gallium arsenide (InGaAs) PIN photodiode. The arrangement is fabricated in two steps. The first step comprises the fabrication of the photodiode through the liquid-phase epitaxy growth process of an undoped indium gallium arsenide (InGaAs) layer of the n type, having a thickness of 3 .mu.m, serving as an active layer, then two thin quaternary InGaAsP buffer layers, followed by an indium phosphide (InP) cap layer. The indium phosphide cap layer is intended to protect the arrangement during the second epitaxial step. During this second epitaxial step the waveguide is deposited on the opposite surface of the substrate by means of three layers, first indium phosphide (InP), secondly InGaAsP (.lambda.g=1.036 .mu.m) and thirdly indium phosphide (InP). The light is guided into the photodiode passing through the whole substrate. For this purpose a facet is formed across the layers forming the guide, underneath the photodiode, by means of anisotropic etching of these layers. The fabrication of the photodiode which is of the PLANAR type further comprises the zinc atom (Zn) diffusion with a 100 .mu.m diameter in the indium gallium arsenide (InGaAs) layer, the external surface passivation by a plasma deposited Si.sub.3 N.sub.4 layer, and the fabrication of the p and n contacts by means of titanium and gold (Ti--Au) metallisation.
The arrangement described in the said document has various disadvantages as to the application considered for detecting the presence of the signal:
in the first place, the detector formed by the photodiode is fabricated on a surface differing from the substrate surface on which the waveguide is fabricated. This is disadvantageous as to the positioning of the substrate in, for example, a casino, or any other supporting element of the substrate;
secondly, the fact that the light beam has to pass through the substrate does not allow the use of very thick standard, semi-isolating substrates of the order of 330 .mu.m;
thirdly, the light reflected by the slab is no longer guided. This arrangement gives rise to losses incrementing with the thickness of the substrate;
in the fourth place, the fact that in the known arrangement the reflected light is not guided does now allow a plurality of arrangements to be positioned next to each other. Actually, in these conditions each arrangement would receive part of the signal meant for the adjacent arrangements. Thus, the known arrangement cannot be used, for example, for detecting the signals at the output of a demultiplixing system, which output is formed by a plurality of light waveguides conveying signals of different wavelengths, because the use of this arrangement would cause undesired multiplexing of these signals;
in the fifth place, the whole signal conveyed by the light wave guide must be transmitted to the detector. This prevents this signal from being used outside this detecting operation, as the known arrangement has only one channel. Consequently, this arrangement is unsuitable for the detection of the simple presence of a signal, for example, as this detection has to be carried out without taking off the whole signal, as the latter is meant for another operation.
It is an object of the invention to provide an arrangement with which these disadvantages can be eliminated.